Blazor Server - downloading excel in the controller

Question

Hi,

In my Blazor Server application, I am trying to write data into Excel and download it in the controller. Here is the controller;

var existingRecords = await _stockUniqueSerialPinUseCase.ExecuteAsync(customerList);
if (existingRecords.Count > 0)
{
       await Export(existingRecords);
}

private async Task Export(List<GameBank> existingRecords)
    {
        ExcelPackage.LicenseContext = LicenseContext.NonCommercial;
        var stream = new MemoryStream();

        using (var package = new ExcelPackage(stream))
        {
            var workSheet = package.Workbook.Worksheets.Add("Duplicate Codes");
            workSheet.Protection.IsProtected = true;

            var recordIndex = 2;

            workSheet.Row(1).Style.Font.Bold = true;
            var headerCells = workSheet.Cells["A1:B1"];
            headerCells.Style.Font.Bold = true;
            headerCells.Style.Font.Size = 13;
            headerCells.Style.Border.BorderAround(ExcelBorderStyle.Thin);
            headerCells.Style.Border.Top.Style = ExcelBorderStyle.Thin;
            headerCells.Style.Border.Left.Style = ExcelBorderStyle.Thin;
            headerCells.Style.Border.Right.Style = ExcelBorderStyle.Thin;
            headerCells.Style.Border.Bottom.Style = ExcelBorderStyle.Thin;
            headerCells.Style.Font.Color.SetColor(System.Drawing.Color.Black);
            headerCells = workSheet.Cells["A1:B1"];
            // Set their background color to DarkBlue.
            headerCells.Style.Fill.PatternType = OfficeOpenXml.Style.ExcelFillStyle.Solid;
            headerCells.Style.Fill.BackgroundColor.SetColor(System.Drawing.Color.LightGray);

            workSheet.Cells[1, 1].Value = "Serial";
            workSheet.Cells[1, 2].Value = "Pin";

            foreach (var duplicate in existingRecords)
            {
                workSheet.Cells[recordIndex, 1].Value = duplicate.coupons.Serial;
                workSheet.Cells[recordIndex, 2].Value = duplicate.coupons.Pin;
                recordIndex++;
            }

            //Make all text fit the cells
            workSheet.Cells[workSheet.Dimension.Address].AutoFitColumns();
            await package.SaveAsync();
        }
        stream.Position = 0;
        var excelName = $"RazerDuplicateCodesList-{DateTime.Now:ddMMyyyyHHmm}.xlsx";


        using var streamRef = new DotNetStreamReference(stream: stream);

        await _jsRuntime.InvokeVoidAsync("downloadFileFromStream", excelName, streamRef);
    }

But I am getting this error; how can I fix this?

JavaScript interop calls cannot be issued at this time. This is because the component is being statically rendered. When prerendering is enabled, JavaScript interop calls can only be performed during the OnAfterRenderAsync lifecycle method.

Answer 1

as the error suggests, move the js interop code to the OnAfterRenderAsync event. as the stream is outside the blazor compoent render process, it makes sense.